1. Field of the Invention
The present invention relates to a method of recognizing identity marks (ID marks) appended on each of a plurality of base materials, a system configured to recognize ID marks appended on the base materials, and a method of manufacturing products by the base materials appended with the ID marks.
2. Description of the Related Art
Usually, in a planned sequence of production processes of a semiconductor device, there are as many as several hundred processes where control of manufacturing conditions and the like are required. In such manufacturing processes of the semiconductor device, various and strict manufacturing conditions must be specified in each manufacturing process. Each of these manufacturing processes is controlled using an ID mark provided on part of a principal side of a semiconductor wafer, including numerals, characters, bar codes, etc.
In recent years, a two-dimensional code implemented by dot marks has been appended as an ID mark on a semiconductor wafer, because the two-dimensional code has a larger data storage capacity than a one-dimensional code, although the marking area required for the two-dimensional code is small, and the two-dimensional code can be formed easily on the semiconductor wafer by a laser delineation technique etc.
A recognizer of the two-dimensional code is adopted for a code recognizer. The code recognizer has an error correction ability by the Reed-Solomon architecture, by which the code recognizer can correct a deteriorated ID mark, in which about 20% to 30% of the ID mark is deteriorated. When recognizing a deteriorated ID mark, the Reed-Solomon architecture rarely makes a mistake in the case where the deteriorated level lies within a range that the error correction ability of the code recognizer can cover.
In U.S. patent application Ser. No. 10/101,337, a method for controlling a sequence of production processes of a semiconductor device is disclosed using an ID mark implemented by a two-dimensional code engraved on a beveled contour of a semiconductor wafer, and by reading the ID mark in each manufacturing process. In U.S. patent application Ser. No. 10/101,337, a plurality of ID marks implemented by two-dimensional dots, which are engraved unevenly on a portion of the beveled contour disposed, are successively added at the perimeter of a notch in the semiconductor wafer along with the proceeding of the process sequence. Then the newest ID mark or all of the ID marks are read by an ID mark recognizing unit, and according to the information on the newest ID mark or all of the ID marks, the semiconductor wafer is processed.
However, in manufacturing processes of a semiconductor device, since an ID mark passes through repeated processes including deposition process of thin films such as insulating film and removal processes such as chemical mechanical polishing (CMP) of the thin films, attachment of particles and damage to dots and the like occur in a certain area of the ID mark or sometimes in a large area over 30% of the ID mark is deteriorated.
In such a case where damage to the ID mark occurs, and exceeds the limit of the error correction ability of the ID mark recognize unit, there is no alternative measure to amend the damage, therefore the ID mark is judged as “illegible” by the ID mark recognizing unit. The semiconductor wafer including the ID mark which was judged as “illegible” has no way but to be removed from the manufacturing line, since the semiconductor wafer with the illegible ID mark can not identify the manufacturing number or the manufacturing process, which results in a decrease in manufacturing yield.
A problem similar to the one mentioned above in the manufacturing method of a semiconductor device occurs in such manufacturing methods where liquid crystal device, magnetic recording medium, optic recording medium, thin film magnetic head, and superconductor elements are manufactured.